There is definitely no excuse for “enterance”. But “thru” and “through” are like “alright” and “all right” in that both are used frequently and cause no ambiguity to a reader.

Check out this example from the Associated Press that uses both variants in the same article (relevant since I deduce from your blog’s history that you respect AP style). The author’s heading reads “Patrons toss dead cat through drive-thru“; the article commences with “An employee working the drive-through window at a McDonald’s will have a tale to tell.”

The natural evolution of language will inevitably either favor one spelling over the other or create a more distinctive purpose for each variant. For now, “through” is the popular choice, and while “thru” may look odd in certain circumstances, the two can be used interchangeably.

The Chicago Tribune at that time was run by a spelling simplification advocate (and those who tried to continue that tradition after he retired). That editor was just one of many people who desired spelling reform, and the Tribune was his little experiment. They stopped using simplified spelling in 1975 because it was awkward and inconsistent. Mark Twain, Noah Webster, and Teddy Roosevelt were other advocates for spelling reform.I approve of ‘thru’ because it omits superfluous letters that no longer hold any literary necessity.